IIRC from a previous employer, they banned bringing cell phones that had a camera into an enclosed area where Secret (= lowest level) documents were in use (specs, drawings, test print-outs, etc.). Removing a Secret document from the enclosed (locked, entry code needed) area, even accidentally could lead to being canned and prosecuted. People allowed to enter the enclosed area had to go through screening to get a clearance.
I didn't have a clearance and worked on non-classified products (microwave power modules).